1. Field of the Invention
The present invention relates to electrical machinery and, more particularly, to homopolar, direct-current motors and generators capable of producing high output torques and high output currents, respectively.
2. Description of the Prior Art
Unipolar, homopolar, or acyclic generators and/or motors are generators/motors in which a unidirectional electromotive force is generated, thus eliminating the need for commutation as is necessary in the ordinary direct current (DC) generators/motors. The operating principles of these homopolar machines are described in such texts as Encyclopedic Dictionary of Electronics and Nuclear, Engineering, by R.I. Sarbacher, Prentice-Hall, Inc., Englewood Cliffs, N.J. (1959), pg. 597-598. An example of such a homopolar machine, in its simplest form, is a Faraday disc generator which is merely a metal disc rotated between the poles of a magnet. Brushes are placed at the rim and center of the disc and an electromotive force is generated in the disc when either a current is applied to the disc or the disc is rotated. Of course, the efficiency of this system is greatly improved if an annular field whose axis passes through the center of the generator shaft is used. When an annular field is used, the electromotive force developed in any ring is constant so that all current paths in the disc are radially oriented. Generally, these machines generate very low electromotive forces even at high speeds and thus, the application of these machines, in their simplest form, has been limited to applications where low voltage and high current are required.
Accordingly, one of the most critical problems confronting designers of high-power electrical machinery has been simplifying their construction while not adversely effecting their ability to produce high powers. In the recent past, those concerned with designing electrical generators having high output currents and motors having high output torques have turned to the use of superconducting magnets. For example, electrical motors having superconducting magnets are currently being considered for ship propulsion where, high torque outputs are critical. Although superconducting machines can serve the purpose in many situations, they are not entirely satisfactory under all conditions of service because of the considerable expense involved in manufacturing and maintaining the superconducting magnets. Such magnets normally include electromagnetic coils made of a special superconductive material that must be kept at relatively low temperatures during machine operation. Further, the added bulk of most superconducting magnets and their power supplies makes their use undesirable in many environments, e.g. aboard ship, where space is critical. It has been recognized, therefore, that electrical motors and generators that employ superconducting magnets, while capable of producing the high magnetic fields required in high-power machines, are relatively more expensive and complicated to manufacture and maintain and more cumbersome to use than are their conventional counterparts.
Consequently, those concerned with the development of high-power electrical machinery have recognized the need for improved techniques of developing conventional-type electrical machinery capable of high-power operation that are not unduly complicated and expensive to manufacture and maintain. The present invention fulfills this need.